Prior to the dawn of civilization, human tribal groups engaged in the rather socialist behavior of sharing food with each other. The concept of sharing food wasn't one of inherent altruism or nobility, however; sharing was a practice that improved the tribes' chances of survival. Without food, a tribe was doomed to wither away. How did the women show their appreciation for the men who brought back meat, and men show their appreciation for the women who collected fruits? By fucking.[1] This exchange of sex-for-food was not a capitalist enterprise—it was just the most fun way of saying "thank you" imaginable. The sharing of sex and food are inherently Darwinian concepts, as both evolved as a means of ensuring survival.

When two tribes encountered each other, since survival was still the primary focus of the tribe, it was not uncommon for them to share what food they could rather than kill each other. Even today, humans generally understand that war is expensive, not just in terms of lives but also in energy, and sharing is less expensive, especially if that sharing will be returned by the continued survival of the benefitters. How did they show appreciation to their benefactors? Guess.

Back then, things were tough, but there was no competition for resources. No one owned the land on which the gazelles grazed, and no one owned the gazelles. The challenge was not in guarding a pasture, but taking a gazelle down so the tribe could eat. When they worked together, everyone benefitted. And everyone pulled their own weight.

Because sex was traded so frequently, fatherhood was hard to establish when women gave birth.[2] This, however, didn't mean the tribe was composed of unwed mothers and deadbeat dads—the offspring became children of the tribe, and their development, disciplining and survival was the responsibility of all the adults who may or may not have shared in the conception of that offspring.[3] Back then it truly did take a village to raise a child.

With the advent of agriculture, humans started guarding the lands they fertilized, thus claiming the resources. This meant a few people in the tribe didn't have to work (hunt and gather)—they just had to hold the resource and let other people do the work (farm). These claims were enforced by might and strength—thus, humans became largely patriarchal. In order to ensure they got meat for themselves and their children, women had to show appreciation to the patriarchs through marriage. Those marriages were often polygamous, depending on the resources the men held. Because of the hoarding, men also needed to ensure that the offspring they were feeding were their own, lest they expend all of their resources too quickly. For the same reasons, men needed to protect their women from other men—practices such as guarded harems, foot-binding and chastity belts came into use.

Over ten thousand years, this collection and hoarding of resources and women, as well as emphasis on patrialineism, has spurred innovation, culture, science as well as othering, religion, and genocide. It is true that without these advances, we wouldn't be discussing this book on the internet, but for all of our advancements, humans may have inadvertently given up one of their strongest talents.

To the typical modern human, this may seem like a utopian fantasy replete with golden age and hunter-gatherer woo. However, it turns out that this view of sexual behavior is not only supported by historical evidence, the tribal culture described above still exists in over two dozen locations around the world, from the Amazon jungle to the South Pacific Islands, to the Inuits in the Arctic north and the mountains of China, despite many centuries of Western and Eastern economic, political and religious influence.

In many of these cultures, there are no concepts of virgin, adultery or rape, and even the concept of marriage, if it exists, lacks the inherent permanence that the Western definition has. Though each culture varies on frequency of "extra-pair bonding" activities as well as the types of activities, they often go way beyond the "new" Western conceptualizations of polyamory or open marriages.

The authors use the word "forager" to describe what is commonly termed "hunter-gatherer", probably because they didn't want to keep typing "hunter-gatherer" to refer to the "cave man" or any of the many tribal cultures that have yet to be assimilated into modern civilization. A decent section of the book is dedicated to dispelling romantic/Victorian era myths and statistical fallacies often associated with early Homo sapiens—some of which would be more appropriate to attribute to earlier humans such as homo habilis, but more likely not.

The authors also use the word "promiscuous" in its scientific definition, meaning "in favor of mixing" as opposed to a "slut". They still use it in terms of sexual mate selection.

The authors discuss the differences between humans and other animals, differentiating mammals from primates from apes. At an evolutionary level, how are humans different? Besides larger brains and the capacity for language, humans have an extreme capacity for sex, as differentiated by distinct anatomical deviations among sexorgans as well as hidden ovulation cycle—that is, human females can and will continue to have sex during their entire menstrual cycle and during pregnancy. Most other mammals, in addition to having sex only for procreation (and not for pleasure), eschew sexual activity during pregnancy.

In other words, the phrase "fucking like animals" should actually be reworded to be "fucking like humans".

In some tribal cultures, both in the present and back before civilization, having sex was as common as a handshake. Women engaged in genital-to-genital contact as a form of bonding (it turns out that even lesbianism is a modern social construct). If the culture was/is a matriarchy, then the men didn't/don't have it so bad—their job consisted of hunting and fucking, and their tribal leaders appreciated and adored their big strong animal killers.

The authors spend quite a bit of time discussing primate evolution and remark that while bonobos are as genetically distant from humans as chimpanzees (that is to say, extremely genetically similar), the studies of chimpanzees tend to trump those of bonobos when drawing comparisons to humans, often because the studies of bonobos are relatively new and not as broad. While it is true that chimpanzees and humans share many traits, including tendencies toward violence and selfishness, on an anatomical and behavioral level humans have more in common with bonobos.[4] In addition to the common behaviors, female bonobos possess a vagina that is farther forward (toward the abdomen) than other apes, and male bonobos have larger testicles than other apes—differences that are also found in humans. Bonobos also share the village mentality, taking care of each others' offspring. Chimpanzees, on the other hand, regularly practice murder and infanticide—as do humans.[5]

The authors quote Charles Darwin and his followers quite regularly—after all, their argument is one of evolution, adaptation, natural selection and progeny—but they point out a fundamental flaw in the assertion that monogamy is an evolutionary construct. Even anthropological experts on the subjects of love and attraction such as Helen Fisher and bonobo experts like Frans de Waal get called out for not completely removing the lens of bias and allowing preconceived notions to cloud their theories. The authors contend that confirmation bias and Victorian era idealism blinds most scientists into seeing monogamy and the nuclear family as evolutionary advantages and not as social constructs.

The authors point out, repeatedly, that if monogamy was an evolutionary advantage, then why are divorce rates increasing in Western society? Why do very few animal species practice true monogamy?[6] Why are children who have a large number of caregivers and teachers better off than the children of single- or two-parent families? Why is infidelity so common, not just in today's "decadent age" but throughout history? Why is there so much competition in mate selection? Why are teenagers getting pregnant? And why is it that after almost two millenia of indoctrination, penance, celibacy and prayer, the Catholic church still can't keep their priests and nuns from getting it on?

Could it be that all the things that religions, conservatives and uptight parents rail against — divorce, prostitution, homosexuality, voyeurism, pornography (which is really just a form of voyeurism), adultery, rape fantasy, bisexuality, polyamory, open marriages, step-parenting, swinging, rap music, rainbow parties, "spin the bottle", communism and orgasms — are really just our human nature trying to come forward and bring us back to tribalism? But it doesn't stop there; tribal human nature also explains generally conservative concepts such as charity, having lots of kids, strong bonds between extended family members, parental reverence, rituals, and homeschooling.

Forget about being rational—does it make fiscal or emotional sense to engage in purity balls, public stonings, peacock-style mate selection competitions, expensive weddings, prolonged loveless marriages, divorce proceedings, custody disputes, exorcisms, genital mutilation, empty promises, reparative therapy or sexual addiction treatment—all things that postpone the inevitable disappointment? Instead of expending so much time, energy and resources trying to not look like a disappointment to our parents, to resist our primal tendancies or to "rise above our nature", wouldn't it make more sense to embrace said nature and just go with it?

A return to such tribal ways away from the "standard narrative", at least when it comes to sexual intercourse and the raising of offspring (the authors certainly don't expect people to give up their cars, computers and cappuccinos), would indeed be a huge paradigm shift. Concepts of envy and greed would need to disappear. Men and women would have to respect each other as equals and be willing to share, in more ways than one. Adults would have to be willing to take care of children that weren't their own, as well as other adults that they only had minor emotional attachments to. Humans everywhere would have to stop listening to their church officials and grandparents. Books and movies that preach "one true love" and "soul mates" would become hokey and/or go away. Randroids would shit themselves. Cats and dogs, living together, it'd be total anarchy!

While the book debunks many myths and misconceptions about sex and relationships, it overplays its hand in a number of areas. Most importantly, while the scenarios and practices that Ryan and Jetha describe likely did occur, there is no way to determine how widespread they were during prehistory with the current evidence available. Indeed, human mating patterns are incredibly variable in the ethnographic record and it is extremely unlikely that there is any universal or "natural" model.[7] Food sharing in central places is often associated with the type of egalitarianism presumed by Ryan and Jetha. Future archaeological findings of central-place sharing would determine how accurate the picture painted in the book is.[8] The claim that bonobos are a better analogy to humans is problematic. Chimps and bonobos are closer to each other than humans and millions of years of history (and thus the evolutionary process) separate us from both of them.[9] The book also cites the "kamikaze sperm hypothesis" as circumstantial evidence, which was controversial at the time of its proposal and now widely considered to be discredited.[10][11] Finally, it is always good to be aware of the fallacy of appeals to nature, or the difference between what is and what ought to be: Just because something's natural doesn't mean it's a good idea. Then again, 'good' is all opinion, anyways, so just go have sex and forget about anthropology.
Also, the authors seem to make the all too frequent assumption that "primitive" cultures of today are more or less exact analogies of early hunter-gatherer cultures, an assumption that rests on the dubious premise that these modern "primitive" cultures have more or less "stood still" or at least changed very little over the millennia. History actually has little to nothing to say about these early cultures beyond what is yielded by archaeology which can't illuminate practices such as gift giving or sex as these leave little in terms of archaeological remains.

↑This led to an interesting familial construct that is often seen as foreign in most non-African cultures: instead of honoring one's father, grandfather or great-grandfather, children in non-Muslim African and some black Caribbean cultures honor their uncle, great-uncle or great-great-uncle, being their mother's brother—that is, a male figure known to be a blood relative. Since many of these cultures tend to be matriarchal, a parallel could be drawn to other black cultures (particularly in the United States) where single motherhood is not uncommon.

↑There is also evidence that suggests a more recent "break"—that is, the most common recent ancestor between humans and bonobos would have lived after the most common recent ancestor between humans and chimpanzees)